Slotted Aloha systems may employ sliding window congestion control with negative or positive acknowledgment. These systems may be inefficient because the retransmission of segments or packets does not take into account the load in the network. Other systems sense whether data is being transmitted prior to sending data segments and/or packets. If data is being sent, then the system backs off and tries again after waiting a random period of time. Such systems require expensive hardware and/or software at the transmitter to sense the network load.